Heat treatment for cylinder block casted with high pressure die-casting

ABSTRACT

Disclosed is a heat treatment method for a cylinder block of an internal combustion engine. More specifically, the method includes heating the cylinder block to a solution heat treatment temperature, processing the cylinder block at the solution heat treatment temperature between 440° C. to 460° C. for one to two hours, quenching the cylinder block and then immediately aging the cylinder block for a predetermined amount of time.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2011-0129698 filed in the Korean Intellectual Property Office on Dec. 6, 2011, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a cylinder block for an internal combustion engine. More particularly, the present invention relates to a heat treatment method of a high pressure casting.

(b) Description of the Related Art

A cylinder block for a vehicle engine is typically manufactured by a sand casting method, a gravity casting method, a low pressure casting method, or a high pressure casting method.

A sand casting methods and gravity casting methods manufacturing a cylinder block that is made of cast iron or an aluminum alloy material typically use pressure from gravity and a feeder. In a sand casting method, the cycle time is typically between 30 to 60 seconds (i.e., a very low characteristic). The sand casting method can use, form and undercut almost any material. However, sand casting is complicated and requires a very large investment cost initially to set up.

Low-pressure casting typically exerts 0.15 to 0.5 bar, and the cycle time is typically about 600 seconds. Thus, even though its recovery rate is quite high, low pressure casting has quite a long cycle time and thus can slow down the overall process.

A high pressure casting method typically uses about 400 to1000 bar, and the cycle time is 50 to 150 seconds. Although high pressure processing allows for high productivity, mass production, and reduced weight, internal bubbles deteriorate a journal portion stiffness particularly when a gasoline engine has increased output.

Therefore products produced via a high pressure casting method have different interior pores from products produced by the low pressure casting and the gravity casting. As a result, heat treatment solutions cannot be applied. That is, when a heat treatment solution is applied to the high pressure casting product, blisters may occurring inside of the product. However, by applying this heat treatment solution, the manufacturer is able to improve the stiffness of the aluminum alloy product. Thus, it is necessary to develop a heat treatment process for aluminum alloy products manufactured using high pressure casting which does not produce blisters on the inside of the product.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide a heat treatment method of a cylinder block having advantages of improving strength and durability by applying an optimized solution heat treatment and an aging treatment.

A heat treatment method of a high pressure casting cylinder block according to an exemplary embodiment of the present invention may include heating the cylinder block to a solution heat treatment temperature, processing the cylinder block in a solution heat treatment temperature that ranges from 440° C. to 460° C. for one to two hours, quenching the cylinder block and then aging the cylinder block.

In some exemplary embodiments, the high pressure casting may be a die casting method, and the heating period at the solution heat treatment temperature may range from 1.5 to 2 hours.

The quenching temperature during the quenching may range from 65° C. to 90° C. After the quenching of the cylinder block, the cylinder block may be aged at a temperature ranging from 150° C. to 200° C. for 2 to 5 hours. A material of the cylinder block may be an aluminum alloy (ADC10).

A heat treatment method of a high pressure casting cylinder block according to an exemplary embodiment of the present invention advantageously improves the strength of the cylinder block that is treated by heat and the durability so that the weight of cylinder block for an internal combustion engine is reduced. Also, the heat treatment method can be widely applied to a cylinder block that is manufactured by high pressure casting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a process of a heat treatment method of a cylinder block according to an exemplary embodiment of the present invention.

FIG. 2 illustrates a heat treatment process of a solution heat treatment and seasoning of a cylinder block according to an exemplary embodiment of the present invention.

FIG. 3 illustrates hardness (rigidity) variations according to seasoning of a cylinder block in an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, referring to the drawings, a heat treatment method of a high pressure casting cylinder block according to an exemplary embodiment of the present invention will be described.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”

FIG. 1 shows a process of a heat treatment method of a cylinder block according to an exemplary embodiment of the present invention. As shown in FIG. 1, a heat treatment method of a high pressure casting cylinder block according to an exemplary embodiment of the present invention includes heating a high pressure casting cylinder block to a solution heat treatment temperature (S10), processing the cylinder block in a solution heat treatment temperature that ranges from 440° C. to 460° C. for one to two hours (S20), and quenching the cylinder block and then aging the cylinder block (S30). The material of the cylinder block may be for example a Japanese industrial standard (JIS) standard aluminum alloy of ADC10.

The solution heat treatment is a process in which a compound of a micro-structure of a casted product or alloy element is mixed with a matrix, and the solution heat treatment temperature is controlled to be within a range of 440° C. to 460° C. so that mixing is possible. The longer the solution heat treatment time is, the better the mixing is, but as stated above a long treatment time increases the cost of production and causes grain growth that deteriorates physical properties of the casting material. Therefore, it is desirable to maintain the treatment preferably for one to two hours. In some exemplary embodiments of the present invention, high pressure casting can be embodied as a die casting method. In this case, the die-casting can be performed in a pressure range of from about 400 to 1000 bar.

FIG. 2 shows a heat treatment process of a solution heat treatment and seasoning of a cylinder block according to an exemplary embodiment of the present invention. In the heat treatment method of FIG. 2, the casted product is heated from room temperature to a solution heat treatment temperature T2. Once T2 has been reached, the solution treatment temperature is maintained for a predetermined time, and then the cast product is quickly cooled (quenched). The quenched product is then heated to an aging temperature (T1) for a predetermined time.

The time required for the cast product to reach the solution heat treatment temperature typically ranges from about 1.5 to 2 hours. This temperature (T2) is then maintained for about another 1.5 to 2 hours at the solution treatment temperature to secure sufficient time for the precipitate in a micro-structure of the cylinder block to be dissolved again

During quenching of the cylinder block, the target temperature ranges from 65° C. to 90° C. As a result, the solid solution of the interior micro-structure of the cylinder block forms a stable precipitate at a cooling temperature by quenching the cylinder block.

After quenching the cylinder block, the cylinder block is aged at a temperature ranging from 150° C. to 200° C. for 2 to 5 hours. When the aging time in the aging temperature exceeds 5 hours, the growth of the precipitate becomes coarse and thus reduces the strength and the elongation of the product, and when the aging time is less than 2 hours, the precipitate is nucleated at a small size. Therefore, the micro-formation of the cylinder block material cannot function as a barrier for preventing dislocation movement, and therefore it is hard to expect a strength increment effect.

A stable precipitate is nucleated to be grown by cooling in the aging temperature, and a driving force of the nucleation is generated at a temperature difference during the quenching at a solution heat treatment temperature.

A diffusional transformation is performed so as to grow the generated nucleate to the precipitate of a predetermined size, heat energy is supplied so that atoms perform lattice diffusion in a solid solution or micro-structure to promote diffusion, and the aging treatment temperature offers an optimized diffusion as a result.

Hereinafter, a heat treatment method of a high pressure casting cylinder block will be described according to an exemplary embodiment of the present invention. However, the below embodiment is an example of the present invention, and the present invention is not limited thereto.

Exemplary Embodiment

A cylinder block for a vehicle is casted by a high pressure die-casting method. The material of the cylinder block is a JIS standard aluminum alloy of ADC30. The cylinder block that is cast by the die casting method is inserted into the induction heating furnace and is heated to 450° C. for 2 hours.

After the cylinder block is heated to 450° C., the temperature is maintained at that temperature (e.g., the solution heat treatment temperature of 450° C.) for 2 hours. The precipitate of the micro-structure of aluminum alloy forming the cylinder block is uniformly distributed in the aluminum alloy matrix as a solid solution state by the solution heat treatment.

After the solution heat treatment, the cylinder block is quickly cooled to 90° C.

Once a quenching temperature is reached, the cooled cylinder block is again immediately heated back to back to 170° C., and the cylinder block is aged at an aging temperature for 5 hours. While the cylinder block is processed during the aging treatment temperature of 170° C. for 5 hours, the nucleate of the precipitate is generated and grows in the aluminum alloy matrix. As a result, in the exemplary embodiment of the present invention, when the micro-structure of the cylinder block created using the aging process described above is checked, no interior defects were found.

TABLE 1 Results showing interior defect of cylinder block in solution temperature and time Solution treatment Solution treatment time temperature 30 minutes 1 hour 2 hours 4 hours 470° C. No No Blister — defect defect 450° C. — No No Blister defect defect

FIG. 3 shows a hardness (rigidity) variation according to seasoning of a cylinder block in an exemplary embodiment of the present invention. More specifically, FIG. 3 shows test results of a cylinder block that is processed in an aging treatment in an aging temperature 170° C. after the cylinder block is processed at a solution heat treatment temperature of 450° C. for 1.5 hours. As shown in FIG. 3, when the aging time is set to 5 hours, the Brinell hardness (BH) thereof is increased to above 115.

Table 2 below shows results when a test material is sampled from the cylinder block created using the aging process above and a tensile test of the test sample is performed as a comparison between a product which was not heat treated and a product that was heat treated.

TABLE 2 A tensile test result of a cylinder block that is not treated by heat and a cylinder block that passes the solution heat treatment and the aging treatment Solution heat treatment Solution heat temperature 450° C., treatment condition No heat treatment duration time 1.5 hours Number of test materials 5 10 Tensile test Max 210 333 result (MPa) Min 201 242 Average 206 272

As shown in the tensile test results of the Table 2, the maximum tensile strength is increased by about 59%, the minimum tensile strength is increased by about 20%, and the average strength is increased by about 32%, when the strength of the test material creating using the above described aging process is compared with the non-treated test material.

As described above, the strength of the cylinder block is increased by the heat treatment according to the present invention to improve the durability and reduces the overall weight of the cylinder block as result.

While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

What is claimed is:
 1. A heat treatment method of a high pressure casting cylinder block, comprising: heating the cylinder block to a solution heat treatment temperature; processing the cylinder block at a solution heat treatment temperature ranging from 440° C. to 460° C. for one to two hours; quenching the cylinder block to a first predetermine temperature; and in response to reaching the first predetermined temperature, heating the cylinder block to a second predetermined temperature and aging the cylinder block for a predetermined amount of time.
 2. The heat treatment method of claim 1, wherein the high pressure casting is a die casting method.
 3. The heat treatment method of claim 1, wherein the solution heat treatment temperature is maintained for 1.5 to 2 hours.
 4. The heat treatment method of claim 1, wherein the first predetermined temperature ranges from 65° C. to 90° C.
 5. The heat treatment method of claim 1, wherein after the quenching of the cylinder block, the cylinder block is aged at a temperature ranging from 150° C. to 200° C. for 2 to 5 hours.
 6. The heat treatment method of claim 1, wherein a material of the cylinder block is an aluminum alloy ADC10.
 7. The heat treatment method of claim 1, wherein the cylinder block is implemented in an internal combustion engine of a vehicle. 